1. Field of the Invention
The present invention relates to a discharge inspection method for a recording head in which recording ink is discharged from a nozzle by an electrothermal energy conversion element applying heat energy on the ink. In addition, the present invention relates to a discharge inspection apparatus for a recording head and a recording apparatus.
2. Description of the Related Art
An inkjet recording apparatus is configured to discharge ink (or an ink droplet for recording) from a nozzle arranged on a recording head. The discharged ink adheres to a recording material, such as a paper sheet, to record various information on the recording material.
An inkjet recording apparatus forms an image by discharging ink from a minute nozzle directly onto a recording material. Therefore, a defective discharge may occur when ink is attached to the surface of a recording head on which the nozzle is arranged (hereinafter referred to as a nozzle surface). For example, when a discharged ink hits a recording material, a part of the discharged ink can bounce off without adhering to the recording material. Moreover, minute ink droplets other than main ink droplets used for recording onto the recording material can be discharged and float in the atmosphere. Accumulation of such ink on the nozzle surface may cause a defective discharge. To prevent such accumulation, the nozzle surface can be treated with a liquid repellant. However, ink residue is difficult to remove completely.
In particular, a defective discharge such as described above tends to occur in a full-line recording apparatus. The full-line recording apparatus includes a plurality of nozzles arranged linearly corresponding to the width of a recording material and can perform recording at high speed. In such an apparatus, a discharge nozzle in which a defective discharge has occurred is quickly identified to conduct recovery of the recording head or to complement image recording.
In an inkjet recording apparatus discussed in Japanese Patent Application Laid-Open No. 07-246708, an optical sensor measures the reflected light intensity of a discharge port surface of a recording head to detect wetness of the discharge port surface. A cleaning unit cleans the discharge port surface according to an output of the optical sensor.
Furthermore, Japanese Patent Application Laid-Open No. 11-179934 discusses an ink jet printing apparatus which is configured to detect dust attached to the bottom surface of a recording head.
In the inkjet recording apparatus discussed in Japanese Patent Application No. 07-246708, the optical sensor can produce an output corresponding to the area of attached ink since wetness is detected with reflected light. However, a small amount of attached ink or an accurate position of the attached ink is difficult to detect.
Moreover, in the ink jet printing apparatus discussed in Japanese Patent Application Laid-Open No. 11-179934, an accurate position of ink attached to the nozzle surface cannot be specified. More specifically, attached ink is detected based on whether a detection light beam is blocked. Consequently, an accurate position of the attached ink in the light path cannot be determined. Therefore, it cannot be determined whether the detected attached ink will clog the head nozzle to generate an ink non-discharge or is located in an area having no nozzle arranged and will not affect the discharge. As a result, each time attached ink is detected on the nozzle surface, a head recovery process such as wiping is always performed. Such process stops printing unnecessarily and degrades throughput performance.
Furthermore, in the ink jet printing apparatus discussed in Japanese Patent Application Laid-Open No. 11-179934, the light path of a light beam is disposed as close to the nozzle surface as possible in order to detect even a small amount of attached ink. Consequently, any convexity which blocks the light beam cannot be formed on the nozzle surface.
Generally, a sealing material seals a joint which electrically joins a head substrate and a wiring material, such as a flexible circuit board. Such a sealing material protrudes 100 to 300 μm from the nozzle surface and is difficult to eliminate at present.